Size of Continents and Seafloor Spreading

Sea Level- Number and Size of Continents

• Pangaea: “supercontinent” that existed 260-240 million years ago
• supercontinents have less coastlines, more harsh continental interiors
  • supercontinents: each of several large landmasses thought to have divided to form the present continents in the geologic past
  • the large landmasses were Gondwana, Pangaea, and Laurasia
• lower species diversity
• extinctions can occur when supercontinents are formed
  • different species on separate continents are forced to compete for food and habitats

Sea Level- Seafloor Spreading Rates

• new oceanic crust is created at divergent boundaries
• the amount of magma that rises and creates new crust at these boundaries changes over geologic time
• more magma = rapid spreading, more mass and volume of new, hot and buoyant rock
  • elevation of seafloor is raised
  • volume of space in ocean basins to hold water is reduced
  • sea level rises

Example: Seafloor Spreading in the Cretaceous

• 110-85 million years ago
• much faster spreading, so there is a lot of new oceanic crust
• global seas level> 660 feet higher than today
• shallow seas covered continents like North America
• the world climate was much warmer than it is today
• the rate of extinction of land-animal species increased

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